Leveling won't be challenging at all, but the thing is... the game isn't really about the leveling at all. That's why we have things like Bind on Account items that grant you a ton of experience. Blizzard realizes that after the first time, it's usually not that special anymore. The only differences you usually get is when you play melee vs ranged (or maybe even healer or tank if you want to level like that).
Another thing I found interesting... it seems Blizzard is very adamant about not changing their pricing for things like faction changes or server transfers. The thing is... reading the stuff above about BoA items and all this other stuff that promotes "Alt-ism", Blizzard essentially pushes us to try and make alts. You eventually get people like me who have 13 80+ characters (6 at 85 I think... I'm bored with leveling though). So when you want to switch... do you give up your other characters? If I wanted to be Horde on another server, it'd cost me $55 per character.
I actually don't mind paying $55 for it, but what I would like is if Blizzard allowed me to tack on more characters at a highly reduced amount. Say maybe $5 more per character. That way, if I wanted to keep my alts, I could do so. I can afford the exorbitant price to do it now, but if I ask myself, "Is it worth over $600 to transfer all of your characters or even $300 to transfer the more important ones?"
Only a lunatic would answer yes.